Conventionally, cutting tools equipped with a coated film formed from ceramics formed on a cemented carbide substrate are well known. In cutting tools used for rough cutting of train wheels and the like, high-strength inserts are used. More specifically, inserts with large nose radii (corner radii), e.g., round inserts, that have undergone honing along the ridge line of the cutting edge are used. Because workpieces such as train wheels are large, variations in stock allowance tend to occur when performing cutting due to hardness variations from quenching and dimension variations from hot forging during production. Thus, there is a demand for inserts with adequate strength to allow stable cutting. Also, inserts with large nose radii make it possible to perform high-efficiency cutting since they result in thinner chips and faster feeding.
Coated cutting tools with surface treatment applied to the cutting edge to provide a stable tool life are also known. For example, Japanese Examined Patent Publication Sho 48-37553; Japanese Laid-Open Patent Publication Number Sho 48-58470; Japanese Laid-Open Patent Publication Number Sho 55-150941; and Japanese Laid-Open Patent Publication Number Sho 60-24371 describe structures in which a ceramic film is not formed on the ridge line of the cutting edge or in which ceramic film is removed from the ridge line of the cutting edge. Japanese Laid-Open Patent Publication Number Sho 59-219122 and Japanese Patent Publication Number 1805360 describe a coated cutting tool in which a ceramic film is thinner at the ridge line of the cutting edge. In Japanese Patent Publication Number 2138025 an aluminum oxide film formed from fine crystals coat the outermost layer. In Japanese Patent Publication Number 2105396 the surface of the ceramic film is smoothed. In Japanese Patent Publication Number 2825693 and Japanese Patent Publication Number 3006453, the ceramic film is formed with different types of film for the outermost layer of the ridge line of the cutting edge and the outermost layer of the other sections.